In the present study the transport phenomena occurring inside a ventilated arc type tunnel greenhouse are simulated during a solar day taking into account the optical properties of plants only in the photosynthetic active radiation (PAR) band. The simulation concerns the day of autumn equinox for an area of central Greece. Two cases are investigated: in the first case the external temperature is considered to be constant while in the second is considered to vary during the day. In order to solve the equations describing the transport phenomena inside the greenhouse a finite volume method is used. Tomato crop inside the greenhouse is simulated as porous material while radiation transport is modelled by the Discrete Ordinates (DO) model. Flow is considered to be incompressible, unsteady and turbulent. From the results it comes out that the consideration of external temperature variation is very important since the internal thermal field is determined by the convection induced by the entering stream except the area covered by a big recirculation in the middle of the greenhouse close to the cover and the close to ground corners where the effect of the entering stream is weak. The distribution of PAR is independent of the external temperature and presents symmetrical time behavior ensuring capable amounts of radiation in all the crops during at least 8 h a day. (C) 2009 Elsevier Ltd. All rights reserved.